The directed assembly of binary blends of diblock copolymers on chemically nanopatterned substrates was investigated as a means to pattern features of controlled dimensions at the nanoscale. The lamella-forming blends assembled without defects and in registration with underlying chemical surface patterns that had periods L-S that were commensurate with the bulk lamellar period of the blends L-B. L-B was tuned between the bulk lamellar periods of the block copolymers L-O1 and L-O2. (c) 2006 American Vacuum Society.